An axle driving apparatus which houses a hydraulic non-stage transmission and axles in a common casing is well known in the art as disclosed in the Japanese Patent Laid-Open Gazette No. Hei 4-92726; U.S. Pat. Nos. 5,090,949; 5,078,659; 4,986,073; 4,914,907; 4,932,209; 4,903,545; 5,010,733; 4,953,426; and Japanese Patent Laid-Open Gazette No. Hei 3-153951.
To simplify construction of the hydraulic non-stage transmission and the axles in the casing, the above-referenced patent documents describe the use of two separate casing members which are coupled along a flat surface to form a single casing. The axis of an output shaft of the hydraulic non-stage transmission and of the axles is contained in tile plane of the coupling surface.
This arrangement has the following disadvantages:
First, when the casing parts are separated for maintenance, all of the interior parts must be disassembled and separated from the casing, and later reassembled following the maintenance.
Second, where the axle driving apparatus is equipped with a braking device, it is usually attached at an output shaft of a hydraulic motor in order to minimize the size of the braking device. The output shaft projects outwardly from the casing, and a brake disc is fixed to the projection. Left and right axles project outwardly from the casing for mounting wheels.
Operating oil used for the hydraulic non-stage transmission or lubricating oil used for the various power transmitting gears is housed in the casing. An oil seal placed on the portion of the output shaft or axle projecting from the casing prevents the oil frown leaking therefrom.
However, because the oil seal spans the two casing members, when there is a tolerance error in manufacturing either the casing or the seal, oil leaks through the coupling surface. As a result, additional means for sealing, such as liquid packing applied to the entire outer periphery of the oil seal, is used to prevent the oil from leaking. This procedure increases the time required to assemble the seal, thus decreasing productivity. Also, this type of seal is expensive to produce.
The third disadvantage is that in hydraulic non-stage transmissions which have an axial piston hydraulic motor, the slanted portion does not reliably bear the thrust of the pistons. This slanted portion, which is subject to the thrust of the pistons, crosses the coupling surface of the casing members. U.S. Pat. No. 4,953,426 discloses additional support for the slanted portion by using integral fingers in the casing which extend from one casing member to the other member across the coupling surface. However, these integral fingers may not be strong enough to bear the thrust of the pistons.